I. Field
The following description relates generally to wireless communications, and more particularly to methods and apparatuses for sequencing and correlating positioning reference signals.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
For many applications it is often desirable to ascertain the location of a mobile device (e.g., user equipment) in a wireless communication system. To this end, trilateration-based downlink positioning techniques can be employed to identify such location. For instance, mechanisms such as Observed Time Difference of Arrival (OTDOA) in Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Networks (UTRAN), Enhanced Observed Time Difference (E-OTD) in GSM (Global System for Mobile) EDGE (Enhanced Data Rates for GSM Evolution) Radio Access Network (GERAN), and Advanced Forward Link Trilateration (AFLT) in CDMA2000 can be utilized to locate a mobile device. For example, OTDOA measurements for a pair of downlink transmissions can describe a line of constant difference (e.g., a hyperbola) along which a mobile device can be located. The position of the mobile device can be identified by determining an intersection between lines of constant difference for at least two pairs of base stations.
A mobile device can estimate time of arrival (TOA) measurements for a set of neighboring cells through replica-based cross-correlation of physical signals transmitted by base stations. Reference signals occur frequently and possess high time-resolution capability. However, auto-correlation functions of reference signals are ambiguous due to time-domain repetition. Positioning performance improves with an increased number of reliable TOA measurements. In dense urban environments, however, a mobile device can reliably receive transmissions from only one or two base stations. Determining position can thus be difficult, which impacts location-based services and emergency call response. Accordingly, it would be desirable to develop a method and apparatus for improving positioning performance via low complexity correlation techniques.
The above-described deficiencies of current wireless communication systems are merely intended to provide an overview of some of the problems of conventional systems, and are not intended to be exhaustive. Other problems with conventional systems and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.